We wish to develop animal models for cellular complement receptors which we will apply to the investigation of receptors in the liver for the complement opsonins, C3b and iC3b. The mechanism by which Kupffer cells (hepatic macrophages) clear soluble antigens and bacteria is presumed to involve cell surface immunologic receptors that recognize opsonins coating those targets. The basis for our inquiry is the finding that complement receptors on monocytes and neutrophils (PMN) reside in an intracellular compartment and can be rapidly recruited to the cell surface by chemotactic peptides and endotoxin, thereby increasing expression of these receptors as much as 10-fold and increasing the capacity of the cell to clear opsonized material. In addition, monocyte complement receptors upon exposure to phorbol esters, acquire phagocytic function. Kupffer cells, the largest pool of tissue macrophages derive from circulating monocytes and may share this inducible property. In the first year, we plan to develop the reagents and methods with which to identify murine complement receptor antigen on the cell surface and receptor-specific mRNA within the cell. In the second year, we wish to determine a) whether unstimulated native Kupffer cell express C3b and iC3b receptors and b) whether in vitro methods for increasing receptor number on monocyte surfaces also apply to Kupffer cells in vitro and in vivo with normal animals. In the third year, we will apply this analysis and resulting method of receptor modulation to a murine model of sepsis (cecal ligation and puncture) to describe the receptor mediated events that occur during sepsis in an attempt to favorably alter survival.